Kovid, Calibre detecs the Fire fine, and sends books to it, fine (though my OCD-ness wishes it put them in the books folder, rather than the docs, lol...but mechanically, as discussed, this is moot, they show up under books tab), but, upon reconnecting, calibre does NOT recognize books that were sent in a previous session (from Calibre) as being on the device -- making both removing them with Calibre, and telling what's on the Fire when connected, problematic.

Yes I noticed the same thing. Once I eject my device (Fire) and reconnect it, Calibre does not recognize that any books are on the device.